Tetra-Ub can be used to investigate mechanisms of binding and recognition by deubiquitinating enzymes, E3 ligases or other proteins that contain ubiquitin-associated domains (UBAs) or ubiquitin-interacting motifs (UIMs). Tetra-Ub is the minimal unit necessary for recognition by the 26S proteasome and contains structural characteristic (such as repeating hydrophobic patches) not present in di-Ub. This product is made with wild-type human recombinant ubiquitin and linkage-specific enzymes, which results in one K63-linkage between two K48-linkages.